1. Field of the Invention
The present invention relates to a print hammer for use in a printing mechanism, and to a method of making the same.
2. Description of the Prior Art
In high speed, moving type, impact printers of the kind typically employed in data processing systems, a separate print hammer is situated at each print position across a row of type. Hammer bank assemblies for this purpose are described in the U.S. Pat. Nos. 3,643,595 to Helms et al and 3,983,806 to Ishi, both assigned to Dataproducts Corporation, the assignee of this case.
Such hammer bank assemblies utilize a plurality of print hammers each having a flat, electrically conductive coil disposed in a generally rigid housing having an impact tip at one end, and supported by a pair of crossed springs at the other end. The springs provide electrical contact to the coil, and aid in restoring the hammer to its rest position subsequent to impact. In the hammer bank assembly, each hammer is situated between a pair of stationarily mounted flat permanent magnets. When a current flows through the coil, the resultant magnetic field interacts with the field of the permanent magnet, resulting in a force which propels the hammer toward the type font and the medium being printed. The basic configuration and operation of such a printing hammer is set forth in the U.S. Pat. No. 3,279,362 to Helms, also assigned to Dataproducts Corporation.
Print hammers and hammer bank assemblies of the type disclosed in the above cited patents have proven to be very effective in use, have exhibited high reliability and long lifetime as measured in number of impact operations between replacement, and have gained widespread acceptance. However, the manufacture of the print hammers themselves is a rather complex process. Typically, it involves the fabrication of ten or twelve fairly complicated individual parts which must be accurately located and assembled in a multi-step process requiring considerable manual labor and expensive fixtures. A principal objective of the present invention is to provide a print hammer having substantially fewer components, and to provide a method of fabrication that is substantially simpler than the prior art.
In a prior art print hammer, a flat coil is sandwiched between a pair of rectangular, rigid, anodized metal plates called "flags". A separate core member was situated in the center of the coil between the flags. A separate terminal board was mounted at one end of the flags. Individual flat wire springs were hooked to terminals on this board. Hard anodizing was used to prevent electrical conduction between the coil, which was electrically connected to the spring wires, and the flags. A complex jig arrangement was necessary accurately to locate the individual flags and associated components while these were joined by appropriate adhesive. Considerable hand labor was necessary to install the individual components in the jig, and to make the requisite mechanical and electrical connections. Once this partial assembly was complete, the individual units were molded to secure in place an impact tip, to embed the terminal board area and its components in a potting compound, and to form a support foot for the flat wire springs.
By contrast, it is an object of the present invention to provide a hammer assembly method in which the unassembled flags, instead of being separate, individual items, are themselves part of an elongated, punched metal strip. The flags are maintained in strip configuration throughout most of the assembly process, thereby facilitating automation of most of the assembly process.
Further objectives of the present invention include the following:
1. the elimination of manual handling of individual hammers;
2. the elimination of components such as the core and terminal board elements of prior art hammers;
3. the elimination of flat wire, formed springs;
4. the elimination of hard anodizing of flags;
5. the replacement of ultrasonic or resistance welding of coil leads by a more controllable joining method;
6. the simplification of production equipment;
7. the elimination of close manufacturing tolerances of certain hammer components;
8. facilitating assembly of a symmetrical hammer from one side only;
9. the reduction of manual finishing operations;
10. reduction of tooling maintenance; and
11. the overall automation of the hammer fabrication process.